Electrical insulation.



part obvious and in WILLIAM H. STEINBERG, 0F MILWAUKEE, WISCONSIN,ASSIGNOR TO THE CUTLER- HAMMER MFG. (10., OF MILWAUKEE, WISCONSIN, A.CORPORATION OF WISCONSIN.

ELECTRICAL INSULATION.

mean-i5.

No Drawing.

To all whom it may concern:

Be it known that LWILLIAM H. STEIN- ennc, a citizen of the UnitedStates, residing at Milwaukee, in the county of Milwaukee and State ofWisconsin, have invented new and useful Improvements in ElectricalInsulation, 'of which the following is a full, clear, concise, and exactdescriptlon.

This invention relates to improvements in composition materialparticularly adapted for electrical insulating purposes.

It has heretofore been roposed to employ a non-inflammable andnon-conducting substance, such as asbestos, as the base for anelectrical insulating material and to mix the same in a comminuted statewith a binder comprising coal tar pitch and one or more solventstherefor. An additional ingredient as a co-binder is usually provided.The resultant mass obtained by this process is molded under pressure andsubsequently baked.

This invention hasamong its objects to provide an improved heatresistant insulating composition of the general character above setforth but which possesses a degree of hardness,'density and mechanicalstrength superior to that heretofore attained. A further object is toprovide an improved binder for combination with a suitable basematerial, such as comminuted asbestos.

Other objects and advantages will be in part specifically notedhereinafter.

As above mentioned, one of the objects of the invention is to provide anim roved cementitious binding compound, and or this purpose there isprovided a mixture of coal tar pitch and stearin pitch, combined insubstantially equal proportions. lit may be mentioned that theseingredients are respectively the residues in the distillation process ofcoal tar and animal fats or vegetable oils and that both are chemicalconglomerates capable of reacting with a variety of other substances.The mixing of the two pitches is preferably carried on in the presenceof heat, or the compound, after mixing, may be subjected to heat. Ineither case the mass is raised to a temperature between 400 and 500 F.and then allowed to cool. During this process, a reaction occurs whichresults in a precipitation of substantially the entire free carboncontent of the coal tar pitch.

Specification of Letters Patent. Patented July 1'7, 191?, Applicationfiled March 1, 1915. Serial No. 11,337.

. The amount of such carbon in commercial grades of coal tar pitchvaries from 10% to 50%, but it is found that usually the carbondeposited equals approximately 30% by weight of the coal tar pitch addedAfter cooling, the supernatant liquid is drawn off and dissolved in asubstantially equal quantity of benzol to which'may be advantageouslyadded small amounts, for example, from 5 to. 15%, of a high boilingnaphtha fraction and a vegetable oil, such as castor oil. Both of thelatter elements serve to stabilize the benzol and thus reduce the rateof free volatilization thereof. Moreover the castor oil also serves anaddi- 'tional purpose as will hereinafter appear.

The insulation base consists of comminuted asbestos as above mentioned,but to which preferably is-added and mixed in a dry state, approximatelyequal quantities of sulfur and one or more metallic peroxide such asbarium or lead. The sulfur and peroxids may be used in small amounts,that is down to about 1}% by weight, of the ground asbestos. I Thismaterial is then gradually mixed cold with a quantity of the abovedescribed binder in a proportion of about four parts of the base to onepart of the binder. Moreover, as above set forth,

. the commingling of the baseand binder is facilitated by the slowvolatilization of the benzol due to the presence of the naphtha andcastor oil.

When these parts are thoroughly mixed, a homogeneous and granular butplastic compound is obtained, which is capable of molding without heatto produce an extremely hard and dense insulation when baked. The

molding is preferably accomplished by compressing the material coldunder from 6,000 pounds to 10,000 pounds pressure after which the moldedarticle is radually heated for approximately twentyour hours to amaximum of from 450 to 500 F. This baking serves to drive 0% byevaporation the entire volatile content of the molded material and alsoefiects a combination, in a manner similar to vulcanizing, of the sulfurmixed with the asbestos and the castor oil in the binder to yield atough, rubbery substance which aids in increasing the mechanicalstrength and toughness of the final product. Furthermore, it is foundthat the metallic peroxid induces increased oxidation of certain of theconstituents of the stearin pitch, in a manner similar to the effect ofan added drier, and thus tends "to harden the product. Moreover, theprecipitation of the free carbon in the coal tar pitch as above setforth, also augments the cementing value of the binder, a resultprobably due to the release of the cohesive force originally expended insustaining the carbon and utilizing the thus released power for bindingthe asbestos particles.

What I claim as new and desire to secure by Letters Patent is 1. Acementitious binder for the purpose set forth including stearin pitchand a volatile solvent therefor.

2. A cementitious binder for the purpose set forth including coal tarpitch, stearin pitch and a volatilesolvent therefor.

3. A cementitious binder for the purpose set forth including coal tarpitch and stearin pitch in substantially equal proportions and a solventtherefor.

4. A cementitious binder for the purpose set forth, including coal tarpitch, stearin pitch and a solvent therefor comprising a volatile oiland a non-volatile oil.

5. A cementitious binder for the purpose set forth includingsubstantially equal parts of coal tar pitch-and stearin pitch and asolvent therefor comprising volatile oil and castor oil.

6. A binder for the purpose set forth, including coal tar pitch, stearinpitch and an oil capable of vulcanization or polymer ization.

7. A plastic composition which is noninflammable and electricallyinsulating comprising a base and a binder the latter including stearinpitch and the admixture of base and binder being molded and baked.

8. A plastic composition which is noninflammable and electricallyinsulating comprising comminuted asbestos and a binder seesaw thereforincluding a mixture of coal tar pitch and stearin pitch.

9. A plastic composition adapted to be molded and baked comprisingcomminuted asbestos having sulfur mixed therewith and a binder includingcoal tar pitch and stearin pitch.

10. A baked plastic composition which is non-inflammable andelectrically insulating comprising comminuted asbestos and a bindersulfur hardened in baking and including coal tar pitch and stearinpitch. 11. A plastic composition to be molded and baked comprising acomminuted asbestos base having mixed therewith sulfur and a metallicperoxid and a binder for said base including coal tar pitch, stearinpitch and a non-volatile solvent.

12. The herein described process which consists in combining under heatcoal tar pitch and stearin pitch, then adding thereto a .solventtherefor and then commingling the mixture with comminuted asbestos.

13. The herein described process which consists in combining under heatcoal tar pitch and stearin pitch, then adding thereto a solventtherefor, then commingling the mixture with comminuted asbestos havingsulfur mixed therewith and then molding and baking the mass.

14. The herein described process which consists in mixing equalquantities of coal tar pitch and stearin pitch, heating the same to 400F., and dissolving the supernatant fluid in a solvent having benzol,naphtha and vegetable oil components.

In witness whereof, I have hereunto subscribed my name in the presenceof two witnesses.

WILLIAM H. STEINBERG. Witnesses:

L. A. WATaoN, Tam Baler.

